Data description

Argo is a real-time global ocean in situ observing system.

Argo is a global network of nearly 4000 autonomous probes measuring pressure, temperature and salinity from the surface to 2000m depth every 10 days. The localisation of these probes is nearly random between the 60th parallels (see live coverage here). All probes data are collected by satellite in real-time, processed by several data centers and finally merged in a single dataset (collecting more than 2 millions of vertical profiles data) made freely available to anyone through a ftp server or monthly zip snapshots.

An example of the Argo cycle program is shown below:

Downloading data

The data registered by each float can be dowloaded from Argo's official website. The data can be downloaded via ftp or http. For this example the float with ID 5906017 was selected and the .nc file was obtained from this link using wget, a Python library.

Reading data

The .nc file is readed with Xarray library. Four tabs are printed: Dimensions, Coordinates, Data variables and Atributes. More specific information is shown in the down drop tabs.

Please check tabs and take a look at all information that you consider important.

Exploring data

Before to start a more-advanced manipulations of this data, it is important to know: what format the data is? If there is time-varying data: What is the data period and frecuency?. In the argo data, 3D variability is expected so a map with the float location in any date is plotted.

The float was drifting in front of the coast of Baja California, México with initial eastward movements. After, westward movements were more frequents. Please note that the donwloaded data covers more than year, in other words, stational variations can be reviewed.

In the next plot, all temperature profiles are shown. Notice that the surface temperature increse during certain times of the year.

The lowest surface temperatures appear to occur during the first months of each year, but this will be analyzed later.

Choosing a profile

In order to verify the temperature data, a random profile is selected and its information is plotted. Profile # 25 is selected and this will be used in future calculations from now on.

The vertical variation of the temperature cooresponds to the temperature profiles for mid-latitude locations are known. The highest values are in the surface due to is the layer that get more radation than other ones. The termhocline, a region which the temperature decreases rapidly, is present in the first 100 meters (it is missing a zoomed axes).

TS diagram

A TS diagram is plotted in order to check the vertical variation of temperature, salinity and finally, density. The density is calculated from the seawater library. Please visit the website for further details.

A decrease in temperature is expected. The salinity has its maximum in the surface where the evaporation take place.The density increases over the deep, temperature and salinity and the values registered are logical

In pursuance of analyzing the static stability with the Argo data explored previously. The concept of Static stability is initially defined and discussed

Static Stability and Brunt Vesala frecuency

\begin{equation} \mathrm{E} = - \frac{1}{\rho} \frac{\partial \rho}{\partial \mathrm{z}} - \frac{g}{C^{2}} \end{equation}\begin{equation} \mathrm{E} \approx- \frac{1}{\rho} \frac{\partial \rho}{\partial \mathrm{z}} \end{equation}

Falta la derivación de la frecuencia de Brunt-vesala

The profile of static stability and Brunt-vesala frecuency is calculated and displayed in the next figure. Although the brun visala frecuency can be calculated with seawater library, the results were obtained from equation number of equation

Description of estimations. Highlight the more important facts

Density profile

It's expected that the density increases with the pressure (deep). Notice that there are regions where the density vertical gradient is larger. Moreover, in deep layers the density vertical gradient is less. In both regions occur different events that will be analyzed with the next animation.

Animation of Static Stability and

Supose that a water parcel is placed in a certain deep in the density profile. If .. (see guide book)